Addition for producing thermally conductive mortars and structural concrete

ABSTRACT

The invention relates to an addition for producing thermally conductive mortars and structural concrete, said addition being a specific powdery formulation in each case, which, when added as an addition to a conventional concrete or mortar, allows the production of a structural concrete or mortar with improved thermal characteristics (thermal conductivity λ). If the addition is added to a conventional concrete in a plant, a structural concrete with increased thermal conductivities is produced, which can adapt to the thermal requirements of the building, thereby being highly suitable for the heat activation of structures or the geothermal activation of foundations. The concrete containing the addition takes on special rheological characteristics which, inter alia, allows a self-compacting concrete to be produced. If the addition is added to a conventional mortar in a mixer, a mortar is produced with very high thermal conductivities which make it highly suitable for geothermal probes.

SECTOR OF THE ART

The invention applies to the construction sector, particularly in thefield of efficiency and sustainability of buildings with thermallyand/or geothermally activated structures.

BACKGROUND OF THE INVENTION

Efficiency and sustainability in buildings pursuant to regulations ordirectives such as European “Directive 2010/31/EU of the EuropeanParliament and of the Council of 19 May 2010 on the energy performanceof buildings,” introduces a new concept, “Nearly-Zero Energy Buildings,”which uses TABS (Thermally Activated Building System) for climatecontrol and cooling, this system consists of the thermal activation ofthe concrete structure of the building, offering a path for the passageof heat to exchangers, which may or may not be geothermal, or both. Theconcretes currently used to activate these structures are the sameconcretes commonly used to build structures, this seriously underminesthe effectiveness of the active structures due to their poor thermalproperties, making it an inadequate product. The reason for thissituation is that any change in the thermal properties of the concretewould cause a considerable loss of mechanical resistance, rendering itsuse as structural concrete impossible, and structural safety mustprevail.

The documents studied, such as US2009294743 and MXPA05011139, describehow to obtain electrically (not thermally) conductive concretes, but donot obtain them by means of an additive, but rather a concreteformulation. Document US2011155019 does use an additive, but forobtaining a concrete resistant to fire and high temperatures. And, interalia, most offer solutions for thermal concretes aimed at improvingthermal insulation by reducing thermal conductivity, as in documentsWO2014006194, CN103570291, CN104108913, WO2013151439, etc., but notincreasing it, precisely the opposite of those obtained in thisinvention. But of all these, none apply the additive solution to theconcrete or mortar to obtain a thermally conductive structural concreteor thermally conductive mortar. The thermal additive is a uniqueproduct, whereby a thermal structural concrete having resistant capacityfor a structural concrete and thermal properties different to those ofany concrete and mortars with very high thermal characteristics areobtained. These properties are especially suitable for use ingeothermally activated foundations with very low enthalpy and/or forthermally activated concrete structures or also for injection mortars ingeothermal probes.

EXPLANATION OF THE INVENTION

The additive is a powdery formulation which, when mixed to manufacture aconventional concrete, makes it possible to obtain a structural concretewith improved thermal characteristics (thermal conductivity λ).Likewise, when mixed with conventional mortars, thermally conductivemortars with very high thermal characteristics are obtained,particularly in the case of injection mortars in geothermal probes.

With respect to the addition of the additive to concrete, depending onthe thermal needs of the building or the characteristics of the terrain,the amount of additive may be increased or decreased or the dosage ofadditive may be modified to adapt the thermal conductivity of theconcrete, but preserving its structural nature. These improved thermalcharacteristics make it highly suitable for the thermal activation ofstructures and/or for geothermal activation in the foundations of abuilding, obtaining greater efficiency and improved sustainabilitythereof.

With respect to the addition of the additive to mortar, depending on thethermal needs of the building or the characteristics of the terrain, thedosage of the additive may be modified to adjust the thermalconductivity of the mortar. These improved characteristics make themortar highly suitable for injection mortars in geothermal probes,although the use of other mortars is not ruled out.

The additive is a product specifically formulated in each case, where byvarying one or several of the components of the additive its propertieswill be modified, particularly the thermal conductivity of the concrete.Said properties may be determined by the specific standards (UNE-EN1745:2013 or UNE-EN 12667:2002).

The thermal structural additive consists of three to six componentsdepending on its application:

-   -   Fine aggregates (calcareous or siliceous) with a grain size of 4        mm, in a proportion that varies between 0% and 95% with respect        to total weight.    -   Fine aggregates (calcareous or siliceous) with a grain size of        less than 0.064 mm in a proportion between 0% and 95% with        respect to total weight.    -   Polycarboxylate ether superplasticizer type powder additive or        derivatives thereof. In a proportion between 0% and 15% with        respect to total weight.    -   Cellulose ether or biopolymer type viscosity modulator or        derivatives thereof. In a proportion between 0% and 10% with        respect to total weight.    -   Natural or synthetic graphite with high thermal conductivity. In        amounts ranging from 0% to 45% with respect to total weight.    -   Graphene and/or carbon nanotubes (nanomaterials) to obtain the        high thermal conductivity characteristics. In amounts ranging        from 0% to 20% with respect to total weight.    -   Some pozzolanic material such as silica fume, pozzolana or fly        ash. In amounts ranging from 0% to 95% with respect to total        weight.

This additive is added in the usual concrete mixer of a concrete planttogether with a conventional concrete which, knowing its dosage (cement,water, coarse aggregates, fine aggregates, additive and/or otheradditives) and mechanical resistance and consistency, the dosage of thethermal additive is adjusted and the amount of additive is determined bym³. If an increase in conductivity is required, the graphite and/orgraphene content would be increased and the fine aggregates would beadjusted to obtain a very compact concrete. It is advisable to use typeI cement (Portland cement). Given the characteristics of the additive,the additivated concrete obtains special rheological characteristicswhich, inter alia, makes it possible to obtain a self-compacting and,therefore, very compact and high-density concrete.

It can also be added to any mortar, but especially injection mortars ingeothermal probes. There is no need to obtain mechanical resistance, butthere is a need to improve thermal characteristics and injectability,therefore the content of fine aggregate is reduced or fully substitutedwith fine aggregates.

PREFERRED EMBODIMENT OF THE INVENTION

Although the possible total dosages may be very high depending on needs,particularly those relating to mechanical resistances andconductivities, a preferred embodiment would be that concrete for thefoundations of a building with geothermia where there is a need toactivate said foundations in order to use the geothermia for efficientand renewable climate control, without heavy investment in a probe fieldto fully supplement climate control and possible sanitary hot water(SHW) needs.

If a conventional concrete typified or designated as HA-30/B/20/IIb isthat used, it is advisable for the cement used to be of the CEM I type;if using a CEM II type cement, preliminary verifications must be made toavoid possible unexpected interactions.

In conventional concrete, it is not necessary to modify the dosage ofthe cement, the usual worksite additives (plasticizers), coarseaggregates and fine aggregates. But the amount of water or w/c(water/cement) ratio is possible to make an adjustment as a consequenceof mixing with the thermal additive.

For each m³ of conventional concrete indicated (2,500 kg/m³), in thispreferred embodiment 50 kg of thermal additive are added per m³ ofconventional concrete.

Thermal additive containing:

-   -   80% of calcareous fine aggregates with a size of less than 4 mm    -   13% of calcareous fine aggregates with a size of less than 0.064        mm    -   1.9% of superplasticizer additive    -   0.1% of viscosity modulator additive    -   5% of finely powdered conductive graphite

When added to the described concrete, a structural concrete with a w/cratio of 0.57 was obtained, with average resistances greater than 55MPa, very dense and self-compacting. The thermal conductivity λ ofapproximately 3.5 W/(K·m) is very convenient for a terrain with highgranite-type conductivity, such as that of the preferred embodiment.

1. An additive for thermally conductive structural concretes andconductive mortars, characterized in that it contains between three andsix components depending on its application, selected from the followingcomponents: Fine aggregate (calcareous or siliceous) with a grain sizeof less than 4 mm, in a proportion comprised between 0% and 95% of totalweight. Fine aggregates (calcareous or siliceous) with a grain size ofless than 0.064 mm, in a proportion comprised between 0% and 95% oftotal weight. Polycarboxylate ether superplasticizer type powderadditive or derivatives thereof in a proportion comprised between 0% and15% of total weight. Cellulose ether or biopolymer type viscositymodulator or derivatives thereof in a proportion comprised between 0%and 10% of total weight. Natural or synthetic graphite with high thermalconductivity in a proportion comprised between 0% to 45% of totalweight. Graphene and/or carbon nanotubes (nanomaterials) to obtain thehigh thermal conductivity characteristics in a proportion comprisedbetween 0% to 20% of total weight. A pozzolanic material such as silicafume, pozzolana or fly ash in a proportion comprised between 0% to 95%of total weight.
 2. The additive for thermally conductive structuralconcretes and mortars, according to claim 1, characterized in that itcontains: 80% of calcareous fine aggregates of a size smaller than 4 mm13% of calcareous fine aggregates of a size smaller than 0.064 mm 1.9%of superplasticizer additive 0.1% of viscosity modulator additive 5% offinely powdered conductive graphite. Obtaining average resistancesgreater than 55 MPa, very dense and self-compacting and thermalconductivity λ of approximately 3.5 W/(K·m).
 3. A method for obtaininggreater or lesser conductivity of the additivated concrete or mortar bymeans of the additive for thermally conductive structural concretes andmortars, according to claim 1, consisting of modifying the indicatedproportions of the additive of claim 1 or adding a greater or lesseramount of additive to the concrete or mortar for thermally conductivestructural concretes and mortars.